Prior to the present invention, a wide range of valve trains with various valve and tappet configurations have been designed for internal combustion engines. A plurality of such valve trains are disclosed on pages 318-319 of Automotive Handbook, 2nd Edition .COPYRGT. Robert Bosch GmbH, 1986 Postfach 50, D-7000 Stuttgart 1, Germany. While these valve trains are satisfactory for their intended applications, they are generally not suitable for use with hemispherical and similar combustion chambers designed for advanced engines and do not provide additional center space in the cylinder head for large, well cooled injection or ignition devices.
In U.S. Pat. No. 5,080,057, issued Jan. 14, 1992 to Batzill et al for "Cylinder Head of an Internal-Combustion Engine", a valve train is disclosed with intake and exhaust valves used with hemispherical combustion chambers that are inclined with respect to axes in the head construction of the engine. To actuate the disclosed valves, inverted bucket tappets are disposed so that they are in coaxial alignment with the valves. With such construction, camshafts with special conical cams or cam lobes are required to properly contact and actuate the valves for effective engine operation. The conical cam lobes of the Batzill construction are complicated and expensive. With such designs, a constant radius base circle on the lobe, requires a minimum tappet diameter increase over the basic tappet diameter of a conventional tappet and cam lobe, at least twice the radial distance between both sides of a conical cam lobe. Such a large tappet diameter, then, is counter-productive, for it forces the center of the lobe to be closer to the longitudinal center of the cylinder and results in less longitudinal plane inclination of the valves and reduced radial angle and curvature in the chamber.
While there are various valve train designs for other hemispherical combustion chambers, such designs usually involve only two-valve operation. Although in these designs both the intake and exhaust valves emanate radially from the combustion chamber, their angularity is only on the transversal plane of the engine. Such designs are disclosed in the valve train design book by Philip H. Smith, C.Eng., M.I.Mech. E., M.S.A.E., "Valve Mechanisms for High-Speed Engines, Their Design and Development", published by Automobile Engineering and printed in 1967 by G. T. Foulis & Co. Ltd., 1-5 Portpool Lane, E.C. 1, London, in association with the Whitefriars Press Ltd., also of London and Tonbridge in the U.K.
This Automobile Engineering publication also shows some designs of hemispherical chambers with four valves, driven by a variety of mechanisms. For example, the Hopwood-B.S.A. single cylinder motorcycle described in page 64 and shown by FIG. 3.23, indicates Single Overhead Camshafts, axially angled with respect to each other and connected by bevel gears, with the axis of each camshaft perpendicular to the single plane connecting each pair of same function valves and driving said valves conventionally by rocker arms operating in the plane of the valve stems.
The four cylinder, four valve per cylinder BMW racing engine of 1967 is also described in the Automobile Engineering publication. In this engine, the four radial valves were conventionally driven by two camshafts via push rods and rocker arms. While the constructions of this publication are of interest, they are not functionally or structurally like that of the present invention.
In addition to the above prior construction, one prior high speed diesel engine for passenger cars featuring a DOHC four valve with indirect injection is described in Automotive Engineering, January 1995 (vol. 103, No. 1), pages 23-25. This publication shows and describes a conventional DOHC, four valve design, with parallel valve stems for each pair of same function valves operating in conjunction with a hemispherical combustion chamber. In this prior design, the valves are angulated with respect to the longitudinal axis of the engine and increased head space is provided. The valves are not angulated with respect to each other in the longitudinal plane. However, the space is inadequate for many engine designs. Accordingly, the illustrated precombustion chamber of this engine is disposed quite far from the main combustion chamber, and is connected to it by a very long transfer passage.
The present invention is readily adaptable to such prior art engines to advantageously provide more room in the center of the cylinder head so that the prechamber can be substantially lowered and the transfer passage can be shorter thereby reducing the volumes outside of the main chamber and increasing the corresponding volumes in such main chamber so that deeper intake valve pockets can be cut on the piston top, allowing the increased intake valve travel at top Dead Center during overlap such as is required by a variable valve timing mechanism. The present invention provides advanced construction augmenting engine operation including cold starting from advanced intake valve closing and the associated increase in Effective Compression Ratio. Besides, with the reduced prechamber and transfer passage volumes and correspondingly reduced heat transfer and pumping losses, the present invention produces increased compression temperatures needed for cold starting and smooth and quiet idle operation.
The Automotive Engineering publication referenced above does not show or otherwise disclose the required shrouding of the heads of the parallel stem valves as they intersect the hemispherical combustion chamber machined in the cylinder head. Such shrouding is shown by FIG. 12, page 329, of an article by Von Ulrich Conrad et al entitled "Die Neuen Viervientil-Diesel Motoren Von Mercedes-Benz", published in the July-August 1993 edition of MTU Magazine (MTZ 54, 1992, 7-8) a technical publication of Motoren-Turbinen Union, a division of Daimler-Benz AG. The disclosed shrouding creates very large and empty pockets which, if the valves were laid-out radially, could be transferred to the top of the piston, thus allowing the installation of the variable valve timing mechanism. Furthermore, this shrouding is so large, taking effect through such a large arcuate section of the valve periphery, that the air flow through the open valve suffers and adversely effects engine operation. Accordingly, and in spite of a very sophisticated air induction system, the rated engine power only increases 20% over the older two-valve engine which the disclosed engine replaces.
In the applicant's invention, a 40% power increase may be readily obtained when applying this invention to four valve technology to replace the older two valve engines. Although intended to create more room so as to allow the placement of the spark plug or other combustion initiation means, the prior designs do not lend themselves to the larger radial angles desired in advanced engine design and as provided by the improvements of the present invention.
The prior designs lacked the slide-pivot articulation of the present invention to open enough center-space for diesel injectors or prechambers due, in some cases, to the placement of the camshaft along the center longitudinal axis of the cylinder head, which would physically interfere, apart from the fact that the valves were not angulated with respect to each other in the longitudinal plane of the engine.
More particularly, and in contrast to the prior constructions, the present invention provides a new and improved valve train that features the effective slide-pivot articulation interconnection of the bucket tappet with an outer end portion of the associated valve stem. This improved interface articulation between the tappet and valve stem allows the tappet to be stroked along a first axis and the associated valve to be stroked along a second axis which radiates from a point within the combustion chamber having a curved interior wall.
The present invention meets higher standards with (1) the provision of a new and improved combustion chamber, preferably hemispherical in configuration, in the head of the engine and (2) intake of air into and exhaust of gas from the engine cylinder by pairs of intake and exhaust valves laid out so that the heads of these valves are substantially tangent to the hemispherical wall of the combustion chamber and so that the stems of these valves extend radially therefrom and outwardly from one another.
The valve stems, accordingly, extend outwardly and preferably with respect to a common point of origin within the cylinder associated with the combustion chamber. The end portions of these stems interface with the inverted buckets or camshaft tappets by slide-pivot and force transmitting construction. With such articulation, conventional actuators, such as DOHC, pivot finger, rocker arms and "T" bridges can be used to displace each of the buckets along a first axis associated therewith and the associated intake or exhaust valve can be displaced along a second and intersecting axis that is coaxial with the radiating valve stem.
With this invention, specially shaped conical cam lobes are eliminated since the face of each cam lobe is generally parallel to the axis of the camshaft and makes full line contact with the tappet. This arrangement may further provide for and feature larger headed intake and exhaust valves resulting in increased and improved cylinder air intake and gas exhaust for improved engine operation. With the improved cylinder head layout, the bridges in the combustion chamber wall between the valve seats are enlarged providing for strengthened constructions. Bridge cooling is also improved since there are increased effective volumes in the water jacket in-between the divergent ports, especially the exhaust ports, in the longitudinal plane.
Another feature, object and advantage of this invention is to provide an internal combustion engine with a generally hemispherical combustion chamber having radiating intake and exhaust valves operated by inverted bucket tappets with internal universal articulation structures so that all the bucket tappets are displaced along parallel first axes while the associated valves are displaced along their respective radiating axes which are angled with respect to the first axes.
These and other features, objects and advantages of this invention will become more apparent from the following detailed description and drawings.